1. Field of the Invention
This invention pertains to a drill for use with flexible materials which are used in the flexographic printing industry. More particularly, it relates to a drill with a single drill head and a video locating device.
2. Discussion of Related Art
Flexographic printing plates are resilient relief image plates made of rubber or photopolymer material, which are used to print on a wide variety of substrates. One critical step in the printing process is the accurate positioning of these printing plates onto the printing cylinder. The printing plate must be positioned such that the printing is parallel to the axis of the cylinder, i.e., not skewed. In multicolor printing, the plates for each different color must be aligned so they print in register. Frequently, this positioning is accomplished using pin registration drilling and mounting devices. The printing plate cylinder is typically removed from the printing press, and the plates are mounted using registration holes often in combination with a separate mounting device. However, for some printing presses, such as those typically used to print corrugated containers, the cylinders generally are not removed from the press. Therefore, the above registration systems cannot be used.
The traditional method for mounting flexographic plates for corrugated printing involves the use of a carrier sheet and a mounter/proofer unit. One or more plates are mounted onto a large flexible sheet known as the carrier sheet, and attached with adhesive or stickyback tape. The carrier sheet is then placed on the printing cylinder in the press. For multicolor printing, the plates for each successive color are positioned on other carrier sheets using a mounter/proofer unit with mirror. This practice is time intensive, highly dependent on the operator's skills, and potentially fraught with errors and inconsistent results. As the demands for improved registration increase, this method becomes increasingly unsatisfactory.
A major advance in the method of mounting plates for corrugated printing was achieved by the introduction of a single-head drill. With this drill, the printer was able to drill registration holes in both the carrier sheet and the plates. The plates were then mounted on the carrier sheet using mounting pins and stickyback tape. Once the plates were mounted, the pins were removed. Thus, the alignment of the plates on the carrier sheet was the same for each color and the need to use the mounter/proofer for mounting was eliminated. Both the speed and the accuracy of the mounting process were improved.
In the above-described apparatus, the alignment means for the drill was a laser light directed at an oblique angle onto the material to be drilled. The operator visually ascertained that the laser light was on the registration target located at the point to be drilled, and then drilled. This visual observation is made without magnification and is potentailly inconsistent. The laser light which shines on the material also scatters, preventing any precise location of the drill lead. Lastly, the position of the laser light relative to the actual drilling site is dependent on the thickness of the material to be drilled. Because the laser light is incident at an oblique angle, with thicker materials, the laser light impinges on the material at a point further removed from the actual drilling site than when thinner materials are drilled. Thus, if the laser is calibrated to focus on the actual drill site using thin materials, when thick materials are to be drilled, the actual drilled hole will be offset from the registration target. For flexographic printing plates, this drilling error results in misregistration of the plates and subsequent loss of quality during printing. Therefore, there exists a need for a drilling and mounting system for flexographic printing plates which overcomes the above disadvantages, especially for use in the printing of corrugated containers.